Simplify the following expression: $z = \dfrac{12a - 20}{-36a - 4}$ You can assume $a \neq 0$.
Explanation: Find the greatest common factor of the numerator and denominator. The numerator can be factored: $12a - 20 = (2\cdot2\cdot3 \cdot a) - (2\cdot2\cdot5)$ The denominator can be factored: $-36a - 4 = - (2\cdot2\cdot3\cdot3 \cdot a) - (2\cdot2)$ The greatest common factor of all the terms is $4$ Factoring out $4$ gives us: $z = \dfrac{(4)(3a - 5)}{(4)(-9a - 1)}$ Dividing both the numerator and denominator by $4$ gives: $z = \dfrac{3a - 5}{-9a - 1}$